Rep. Joe Hoeffel has decided to enter the 2004 Pennsylvania Senate race, sources said Friday, although a formal announcement from the three-term Democrat is not expected before next month.

While the lawmaker’s office would not confirm that Hoeffel is definitely in the race, sources said he has begun telling people that he will seek his party’s nomination next year in hopes of facing either Sen. Arlen Specter or Rep. Pat Toomey, who are squaring off in a GOP primary.

Regardless, Hoeffel’s entrance into the contest greatly boosts Democratic hopes of mounting a competitive race in a key presidential swing state. It also is yet another headache for House Democrats as they struggle to win back the chamber.

“We aren’t saying a decision has been made,” Hoeffel spokesman Frank Custer said Friday. “We believe that he will announce for Senate in the near future, but he is not making an announcement today and won’t for the next couple of weeks anyway.”

Custer added: “But he believes that it will happen.”

Sources indicated that Hoeffel will formally announce his candidacy by early to mid-July, possibly as soon as Independence Day.

One source familiar with Hoeffel’s thinking said the timing of the announcement was more a matter of logistics than anything else at this point.

“My understanding is, you know, he’s moving forward and it’s just now a matter of coordinating [Pennsylvania Gov. Ed Rendell’s (D)] schedule and some other scheduling things to get the formal announcement to happen,” the source said. “I think it’s more logistics than holdups.”

Rendell’s support is considered crucial in the race, and sources said Hoeffel has gotten assurances that the governor will be firmly behind him. There had been some speculation in Democratic circles that Rendell might provide only tacit support for the party’s Senate nominee because of his close relationship with Specter. The four-term Senator hired Rendell as an assistant district attorney in the late 1960s while serving as Philadelphia district attorney, and the two have remained close friends since.

“Rendell’s the governor now and he wants to be a big player in the Democratic Party,” said the source familiar with Hoeffel’s thinking. “He’s got to get behind Democratic candidates, and I think he’s made clear to the Congressman that he’s going to be with him.”

Recent polling conducted on behalf of Hoeffel by the Democratic Senatorial Campaign Committee showed Specter’s re-election numbers “well below” the 50 percent mark, according to one Democratic source familiar with the poll, which was conducted by prominent Democratic pollster Mark Mellman.

“This poll was designed to kind of get him there,” the source observed.

A source close to Hoeffel cited the recent polling, the weak economy and the belief that Specter will be bloodied in the primary as factors that led to the Congressman’s decision.

“We believe Senator Specter is vulnerable,” the source said. “Congressman Toomey is a real threat in the primary.”

Toomey, a restaurateur who was elected in 1998 and pledged to serve only three terms, last week received the endorsement of National Federation of Independent Business Chairman Tom Musser.

Still, Specter, who has the backing of the White House and GOP Senate leaders, is heavily favored to win the primary. He had $7 million in the bank at the end of March and recently netted $200,000 at a Harrisburg fundraiser with Vice President Cheney.

Heading into the cycle, Specter appeared in strong position to win a fifth term, and Democrats faced some difficulty as they tried to spawn interest in the race. While a number of potential Democratic candidates had been mentioned, the only other person to express interest in running is John Hanger, the leader of an environmental advocacy group.

The source close to Hoeffel dismissed speculation that Hoeffel, whose name had previously been mentioned as one of several Democrats interested in challenging Sen. Rick Santorum (R-Pa.) in 2006, was entering the race in part to better position himself up for a future statewide run.

“That is not what’s driving this decision,” the source said. “If he runs in 2004 it’s because he thinks he can win in 2004. It’s not because he thinks he’s setting himself up for 2006.”

Meanwhile, Hoeffel’s exit from the 13th district leaves Democrats with a competitive open seat to defend and assures the Keystone State of at least two nationally targeted races in 2004.

In Toomey’s swing 15th district, Republicans have unified behind state Sen. Charlie Dent (R), while Democrats are still searching for a candidate.

Vice President Al Gore carried both districts on his way to winning a 51 percent to 46 percent victory in the state, although the districts are considered highly competitive by both parties. The 13th district was made more Democratic during redistricting by merging the wealthy Montgomery County suburbs Hoeffel represented with a chunk of Northeastern Philadelphia represented by then-Rep. Bob Borski (D). Borski chose to retire rather than face Hoeffel in a primary.

As news of Hoeffel’s decision spread late last week, former Chief of Staff Josh Shapiro became the first Democrat to say he is thinking about running for his old boss’ seat.

“I am seriously considering it,” said Shapiro, who turned 30 on Friday.

Shapiro, now a Philadelphia attorney, left the office in April after spending four years as Hoeffel’s top aide.

Other potential Democratic candidates mentioned include Borski, who is now lobbying in D.C. on behalf of Rendell’s administration, former Philadelphia City Manager Joe Martz and Philadelphia City Controller Jonathan Saidel.

On the Republican side, state Rep. Ellen Bard (R) is the only announced candidate currently in the race. Other possible GOP contenders include ophthalmologist Melissa Brown, who lost to Hoeffel 47 percent to 51 percent in 2002, Montgomery County Commissioner Jim Matthews and former Rep. Jon Fox, whom Hoeffel defeated in 1998.

When he announces, Hoeffel will become the seventh House Member, and first Democrat, all but certain to seek a Senate seat in 2004. At least two other Democrats in competitive districts, Reps. Alan Boyd (Fla.) and Brad Carson (Okla.), are among those still mulling Senate bids.